1. Field of the Invention
The present invention relates to a turbocompound internal combustion engine, in particular for automotive vehicles, more specifically for industrial vehicles, provided with a heat recovery system.
2. Prior Art
In automotive engines, in particular large diesel engines, such as those for heavy vehicles, the thermal energy of exhaust gases from the engine is recovered in turbines positioned on the exhaust line. The turbines can be utilized to drive compressors positioned on the suction line for supercharging. In turbocompound engines a turbine, usually positioned downstream of a supercharger turbine, supplies mechanical power to the engine through the drive shaft and with a suitable transmission and reduction system, owing to the fact that the rotation speed of the turbine is usually much higher than that of the engine (a few tens of thousands of revolutions per minute), to obtain adequate outputs. In this way performances are improved, also in relation to the production of pollutants.
In any case, the thermal energy is not completely recovered. Even by expanding the gases to the pressure at which they are sent to any treatment systems to be discharged into the environment, they still have residual heat, in the form of sensitive heat (i.e. temperatures even in the order of 300-500° C.). To recover this heat, systems have been utilized in which the heat is transferred, in an exchanger, to a fluid belonging to a closed circuit, equipped with a secondary turbine in which the fluid is expanded recovering power which is usually utilized in an electric generator. The fluid is then recirculated with suitable means to the heat exchanger. If the fluid can be liquefied the heat exchanger is an evaporator. These systems are known and do not require further description.
The use of the secondary turbine to generate electrical energy creates the problem of an increase in the overall dimensions and complexity of the system. It would be desirable to be able to recover heat in a simple and efficient way, utilizing structures already present in the engine apparatus.